The objective of this study is to define host functions involved in integration of coliphage lambda and other transposable genetic elements (such as Insertion Sequences (IS), antibiotic markers and other temperate phages) into the bacterial chromosome. The primary approach will be genetic. Toward this end we have developed a technique which aids in the selection of Escherichia coli host mutants (him)in which integration of phage lambda is restricted. In order to characterize the mutants and determine if the mutations involved define genes coding for functions essential for integrative recombination we propose the following studies: 1) Each mutation will be mapped and its dominance pattern determined. 2) The effect on lambda integrative recombination will be quantitatively assayed 3) The level of integration of other elements will be measured. 4) Excision frequencies of various genetic elements will be determined. 5) We will select for second site mutations which suppress the initial him mutations. 6) Since phage Mu appears to require integration for growth, we propose to study growth of Mu in him mutants. Not only should these studies yield direct knowledge about the integration of lambda as well as transposable elements such as antibiotic resistance factors, but they should have general application in understanding the process of viral induced malignant transformation. Moreover, mutations reducing integration should be useful in the construction of safer hosts for propagation of recombinant DNA.